Preoxygenation was performed with the 60 volunteers placed in the supine position with 100% oxygen. All volunteers went though preoxygenation with two techniques: 1) breathing normal tidal volumes at a normal respiratory rate for a period of 5 minutes through a tight fitting conventional face mask, and 2) eight deep breaths (i.e. vital capacity breaths) through the UMOX device with verbal indication to use only the mouth to breathe.